Reflow soldering apparatus and method

ABSTRACT

The present invention provides an apparatus and a method for operating reflow soldering in a mounting field whereby an abnormality in transfer of circuit boards can be detected with high reliability. Whether or not a circuit board is transferred by a transfer conveyor is judged. A discharge conveyor is started when a control device judges occurrence of transfer abnormality. After the discharge conveyor starts, the transfer abnormality is determined to be a drop of the circuit board if a discharge completion detector detects that a dropped circuit board is discharged. And then the control device continues the reflow soldering. The transfer abnormality in the reflow soldering apparatus can be detected with high reliability because it can be detected whether the transfer abnormality is either the drop or a clog of the circuit board.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflow soldering apparatus and areflow soldering method for soldering electronic components on a circuitboard by sending the circuit board with electronic components mountedthereto through a heating furnace.

2. Description of the Related Art

In a reflow soldering apparatus, a circuit board and electroniccomponents are heated, thereby melting a solder to join the circuitboard and electronic components by the solder. A high reliability hasbeen demanded recently in judging whether the circuit board istransferred normally or abnormally in the reflow soldering apparatus toprevent overheating of the circuit board and the electronic componentsduring the transfer.

A conventional reflow soldering apparatus will be described withreference to FIG. 12. In a conventional reflow soldering apparatus 1shown in FIG. 12, 2 is a circuit board, 3 is a circuit board transferconveyor, 4 is a controller, 5 is a reception side of a transmittingtype sensor, and 6 is a projection side of the transmitting type sensor.Operation of the reflow soldering apparatus in the constitution will bedescribed below.

The circuit board 2 carried in from an entrance side 7 of the reflowsoldering apparatus 1 is transferred to an exit side 8 of the reflowsoldering apparatus 1 by the circuit board transfer conveyor 3. If thecircuit board drops from the circuit board transfer conveyor 3 whilebeing transferred, the reception side 5 and projection side 6 of thetransmitting type sensor detect the dropped circuit board 2, withoutputting a signal to the controller 4.

Meanwhile, a publication No. 4-356352 of Unexamined Japanese PatentApplication discloses a reflow soldering apparatus which has circuitboard-detecting sensors arranged at an entrance and an exit, and circuitboard surface temperature-detecting sensors arranged via a constantinterval thereinside. It is monitored whether the sensors are turnedinto an off state within a fixed time after having been an on state inconsequence of detecting the circuit board, thereby detecting whether ornot the circuit board is caught in the middle of the transfer.

In the above constitution of the reflow soldering apparatus 1 shown inFIG. 12, only the drop of the circuit board 2 is detected and a jam ofthe circuit board in the middle of the transfer cannot be detected.Also, since the transmitting type sensor is used to detect the drop, theapparatus 1 has a problem that the circuit board 2 that is detectable inthe apparatus is limited in terms of a thickness by a light projectionwidth from the transmitting type sensor.

Further the invention disclosed in the published specification No.4-356352 cannot detect the drop.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a reflowsoldering apparatus and a reflow soldering method with which anabnormality in transfer of circuit boards can be detected with highreliability, with solving the above problems.

In order to achieve the aforementioned objective, according to a firstmode of the present invention, there is provided a reflow solderingapparatus comprising:

a transfer conveyor for transferring a circuit board with electroniccomponents from an entrance to an exit of the reflow soldering apparatushaving a heating furnace through which the circuit board mounted ispassed so as to operate reflow soldering to the electronic components onthe circuit board;

an exit-side circuit board detect sensor arranged at the exit fordetecting that the circuit board transferred by the transfer conveyor iscarried into the reflow soldering apparatus;

a discharge conveyor arranged below the transfer conveyor fordischarging a dropped circuit board dropped from the transfer conveyorduring the transfer by the transfer conveyor from an inside to anoutside of the reflow soldering apparatus;

a discharge completion detector arranged at an exit side of thedischarge conveyor for detecting that the dropped circuit boardtransferred by the discharge conveyor is discharged to the outside ofthe reflow soldering apparatus; and

a control device which judges based on information from the exit-sidecircuit board detect sensor whether or not the circuit board istransferred by the transfer conveyor from the entrance to the exit,controls the discharge conveyor to discharge the dropped circuit boardwhen judging occurrence of transfer abnormality, determines that thetransfer abnormality is the drop of the circuit board when the dischargecompletion detector detects the dropped circuit board, and thencontinues the reflow soldering when determining the drop.

In an arrangement of the reflow soldering apparatus, in the case where aplurality of circuit boards are carried to the entrance in a singleline, the control device may determine that the transfer abnormality isa jam of the circuit boards at the transfer conveyor and then lowering atemperature of the heating furnace when the dropped circuit board andmoreover the exit-side circuit board detect sensor does not detectdischarge of the circuit board.

The reflow soldering apparatus may further comprise an entrance-sidecircuit board detect sensor arranged at the entrance for detecting thatthe circuit board is carried into the apparatus, wherein the controldevice has a transfer estimate time necessary for the transfer conveyorto transfer the circuit board from the entrance to the exit, so that thecontrol device judges presence or absence of the transfer abnormality ona basis of whether or not the exit-side circuit board detect sensordetects discharge of the circuit board within a circuit board detecttime after the transfer estimate time has passed, the circuit boarddetect time corresponding to a passing time of the circuit board in atransfer direction of the circuit board detected by the entrance-sidecircuit board detect sensor.

In the reflow soldering apparatus may further comprise an entrance-sidecircuit board detect sensor arranged at the entrance for detecting thatthe circuit board is carried into the apparatus, wherein, in the casewhere a plurality of circuit boards are carried to the entrance in asingle line, the control device judges presence or absence of thetransfer abnormality based on a comparison between a carry-in intervalof adjacent circuit boards detected by the entrance-side circuit boarddetect sensor and a discharge interval of the adjacent circuit boardsdetected by the exit-side circuit board detect sensor.

The reflow soldering apparatus may further comprise an entrance-sidecircuit board detect sensor arranged at the entrance for detecting thatthe circuit board is carried into the apparatus, and

a counter device in which a circuit board count set value is defined andwhich adds one when the entrance-side circuit board detect sensordetects the circuit board and subtracts one when the exit-side circuitboard detect sensor detects the circuit board, the circuit board countset value corresponding to the number of circuit boards which can bepresented between the entrance-side circuit board detect sensor and theexit-side circuit board detect sensor,

so that the control device judges presence or absence of the transferabnormality on a basis of a comparison between the circuit board countset value and a counted circuit board value by the counter device.

Further according to a second mode of the present invention, there isprovided a reflow soldering method comprising:

judging whether or not a circuit board with electronic componentsmounted thereon is transferred by a transfer conveyor from an entranceto an exit of a reflow soldering apparatus with a heating furnace foroperating reflow soldering to the electronic components on the circuitboard by passing the circuit board through the heating furnace;

detecting, when presence of transfer abnormality is judged, whether ornot a dropped circuit board dropped from the transfer conveyor whilebeing transferred by the transfer conveyor is discharged to an outsideof the apparatus by a discharge conveyor arranged below the transferconveyor;

determining, when the dropped circuit board is detected to be dischargedby the discharge conveyor, that the transfer abnormality is the drop ofthe circuit board; and

continuing the operation of the reflow soldering.

In the reflow soldering apparatus according to the first mode and thereflow soldering method according to the second mode of the presentinvention, the transfer conveyor, the exit-side circuit board detectsensor, the discharge conveyor, the discharge completion detector, andthe control device are comprised in addition to the heating furnace forsoldering. Whether or not the circuit board is transferred by thetransfer conveyor is judged, and the discharge conveyor is started whenan abnormality in the transfer is judged. After the start of thedischarge conveyor, when the discharge completion detector detects thatthe dropped circuit board is discharged, the transfer abnormality isdetermined to be the drop of the circuit board and the reflow solderingis continued. Thus it can be detected whether the circuit board transferabnormality in the reflow soldering apparatus is the drop of the circuitboard or the clog of the circuit board. The transfer abnormality is thusdetected with high reliability.

Since the heating furnace is decreased in temperature when the circuitboard clog is judged, the clogged circuit board is prevented from beingexcessively raised in temperature.

Further, in the reflow soldering apparatus according to the first mode,since presence or absence of the transfer abnormality is judged on thebasis of the transfer estimate time, the transfer abnormality of thecircuit board can be detected irrespective of a thickness of the circuitboard.

Further, in the reflow soldering apparatus according to the first mode,when the judgment is based on the comparison between the carry-ininterval and discharge interval of the circuit boards, the presence orabsence of the transfer abnormality can be judged for each transferredcircuit board.

Further, in the reflow soldering apparatus according to the first mode,when the presence or absence of the transfer abnormality is judged onthe basis of the number of circuit boards being transferred, thetransfer abnormality can be detected irrespective of thicknesses of thecircuit boards and, whether the transfer abnormality results from theclog or drop in the middle of the transfer of the circuit boards by thetransfer conveyor can also be judged.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings in which:

FIG. 1 is a diagram schematically showing the constitution of a reflowsoldering apparatus according to a first embodiment of the presentinvention;

FIG. 2 is a flow chart of an operation for detecting the presence orabsence of transfer abnormality by the reflow soldering apparatus shownin FIG. 1;

FIG. 3A is a diagram explanatory of a circuit board length measurementoperation in FIG. 2;

FIG. 3B is a diagram showing a change in output signal of anentrance-side circuit board detect sensor because of the circuit boardlength measurement operation;

FIG. 4 is a flow chart of an operation for processing the transferabnormality in each embodiment of the present invention;

FIG. 5 is a diagram schematically showing the constitution of a reflowsoldering apparatus according to a second embodiment of the presentinvention;

FIG. 6A is a diagram explanatory of an operation for measuring a circuitboard carry-in interval in the reflow soldering apparatus of FIG. 5;

FIG. 6B is a diagram showing a change in output signal of theentrance-side circuit board detect sensor because of the measurementoperation for the circuit board carry-in interval;

FIG. 7 is a flow chart of an operation for detecting the presence orabsence of transfer abnormality by the reflow soldering apparatus shownin FIG. 5;

FIG. 8 is a diagram schematically showing the constitution of a reflowsoldering apparatus according to a third embodiment of the presentinvention;

FIG. 9 is a diagram explanatory of an operation for counting the numberof circuit boards in the reflow soldering apparatus shown in FIG. 8;

FIG. 10 is a flow chart of an operation for detecting the presence orabsence of transfer abnormality by the reflow soldering apparatus shownin FIG. 8;

FIG. 11 is a diagram of an arrangement relationship in a thicknesswisedirection of the circuit board between a transfer conveyor and adischarge conveyor in each embodiment of the present invention;

FIG. 12 is a diagram schematically showing the constitution of aconventional reflow soldering apparatus; and

FIG. 13 is a perspective view of a transfer conveyor provided in eachembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A reflow soldering apparatus and a reflow soldering method carried outby the reflow soldering apparatus of embodiments of the presentinvention will be described with reference to the drawings. It is to benoted here that like parts are designated by like reference numeralsthroughout the drawings.

First Embodiment

FIG. 1 shows the total constitution of a reflow soldering apparatus 101according to a first embodiment. The reflow soldering apparatus 101includes a transfer conveyor 110, an exit-side circuit board detectsensor 112, a circuit board discharge conveyor 115, a circuit boarddischarge completion detect sensor 117, a control device 118, and aheating furnace 122. The reflow soldering apparatus further has anentrance-side circuit board detect sensor 111, a speed detector 116 forthe transfer conveyor, a driving source 119 for the transfer conveyor, adriving source 120 for the circuit board discharge conveyor, and adisplay device 121.

The transfer conveyor 110 transfers a circuit board 2 with electroniccomponents 9 mounted thereto from an apparatus entrance 131 of thereflow soldering apparatus 101 to an apparatus exit 132. The transfer iscarried out by the driving source 119 of a motor in the embodiment. Asshown in FIG. 13, the transfer conveyor 110 is a chain conveyor with apair of chains 1101. Each chain 1101 has supporting pins 1104 setprojecting slightly in a breadthwise direction 1103 of the circuit board2 which is orthogonal to a transfer direction 1102 for the circuit board2. The circuit board 2 is placed on the supporting pins 1104, therebybeing supported at both end parts thereof by the supporting pins 1104 asindicated in FIG. 11. The circuit board is transferred as the chains1101 move in the transfer direction 1102. At least one of the chains1101 is moveable in the breadthwise direction 1103 to meet a breadth ofthe circuit board 2, so that various circuit boards 2 can betransferred.

The speed detector 116 is set to the driving source 119, and a signalrelated to a transfer speed of the transfer conveyor 110 detected by thespeed detector 116 is supplied to the control device 118 which controlsthe driving source 119 with a feed-back control.

The entrance-side circuit board detect sensor 111 is constituted of areflecting type photoelectric sensor in the present embodiment, andarranged at the apparatus entrance 131 for detecting when the circuitboard 2 is carried into the reflow soldering apparatus 101. Theentrance-side circuit board detect sensor 111 is used in the embodimentalso for measuring a length of the circuit board along the transferdirection of the carried circuit board 2.

The exit-side circuit board detect sensor 112 is constituted of areflecting type photoelectric sensor in the embodiment, which isarranged at the apparatus exit 132 to detect when the circuit board 2 iscarried out of the reflow soldering apparatus 101. The entrance-sidecircuit board detect sensor 111 and the exit-side circuit board detectsensor 112 send detect signals to the control device 118.

In the halfway of a transfer path of the transfer conveyor 110 isinstalled the heating furnace 122 for heating both the circuit board 2with electronic components 9 and the electronic components 9, meltingsolder thereby soldering the electronic components 9 on the circuitboard 2. The heating furnace 122 is provided with a heater 1221 forheating and a fan 1222 for circulating gas heated with the heater 1221within the heating furnace 122 as indicated in FIG. 1.

The transfer conveyor 110 supports the circuit board 2 by the supportingpins 1104 projecting in the breadthwise direction 1103 as mentionedbefore. Also, a contact area of each side on the circuit board 2 whichcomes into contact with the supporting pins 1104 should be an area notforming conductor traces on the circuit board 2, and should be as narrowas possible because of high-packaging density of the circuit board.Therefore a standard circuit board has a 3 mm-width in each contact areain the breadthwise direction 1103 and even a nonstandard circuit boardhas a 4-5 mm-width. Further since the transfer conveyor 110 is, forexample, a several meters long, each chain 1101 of the transfer conveyor110 is unfavorably moved about 1 mm in the breadthwise direction 1103.Further the circuit board 2 becomes deformed in various shapes, forexample, in warpage, twisting or the like due to heat of the reflowoperation. Under the above circumstances, even if a gap between thechain 1101 and each side face of the circuit board 2 is set to be inabout 0.5 mm in the breadthwise direction 1103, when the transferconveyor 110 is expanded in breadth by heat of the reflow operation, thecircuit board 2 supported by the transfer conveyor 110 might drop fromthe transfer conveyor 110.

Thus, as shown in FIG. 11, the circuit board discharge conveyor 115 isarranged directly below the transfer conveyor 110 in a verticaldirection along with the transfer conveyor 110. The circuit boarddischarge conveyor 115 is formed in a belt-type conveyor receiving adropped circuit board 133 dropped from the transfer conveyor 110 duringthe transfer by the transfer conveyor 110, and discharges the droppedcircuit board 133 outside of the reflow soldering apparatus 101. In theembodiment, the driving source 120 for the circuit board dischargeconveyor 115 which is a motor is controlled by the control device 118 tooperate to transfer the dropped circuit board 133. The circuit boarddischarge conveyor 115 has a breadth not smaller than a breadth of thetransfer conveyor 110 as is clear from FIG. 11. Although the circuitboard discharge conveyor 115 extends over an entire length of thetransfer conveyor 110 according to the embodiment, the circuit boarddischarge conveyor 115 may be omitted at a place where the circuit board2 never drops at all. Since the transfer conveyor 110 has its sizechangeable in the breadthwise direction 1103 as described before, thebreadth of the circuit board discharge conveyor 115 is designed toexceed a maximum changed breadth of the transfer conveyor 110. Asillustrated in FIG. 11, a drop prevent wall 1151 may be arranged at eachside of the transfer discharge conveyor 115 to prevent the droppedcircuit board 133 dropped on the circuit board discharge conveyor 115from dropping further out of the transfer discharge conveyor 115.

The circuit board discharge completion detect sensor 117 consists of alimit switch in the embodiment. The sensor detects whether or not thedropped circuit board 133 is discharged out of the apparatus by thecircuit board discharge conveyor 115 and sends a detect signal to thecontrol device 118.

The display device 121 is a device for visibly displaying a kind of anabnormality when the circuit board 2 is transferred abnormally by thetransfer conveyor 110.

In the first embodiment, the control device 118 is provided with amemory part 1181 and a monitor part 1182. The memory part 1181 stores atransfer estimate time which is a period after the entrance-side circuitboard detect sensor 111 completes to detect the circuit board 2 beforethe exit-side circuit board detect sensor 112 starts to detect thecircuit board 2 transferred by the transfer conveyor 110. The monitorpart 1182 measures an actual transfer time actually required from theabove detect completion to the detect start.

The operation of the reflow soldering apparatus 101 in the firstembodiment constituted as above will be described below. The operationdepicted below is controlled by the control device 118. The solderingoperation by the heating furnace 122 is not different from that executedby a heating furnace of the conventional reflow soldering apparatus andtherefore, the soldering operation will not be discussed in eachdescription of the first through a third embodiments hereinbelow.

In step (designated in the drawing by “S”) 1 in FIG. 2, the drivingsource 119 for the transfer conveyor drives the transfer conveyor 110 inresponse to a command from the control device 118. A speed of thetransfer conveyor 110 is calculated through the speed detector 116 bythe control device 118 and set to a predetermined value.

When the entrance-side circuit board detect sensor 111 detects thecircuit board 2 carried in from the apparatus entrance 131, in step 2,the control device 118 measures a circuit board detect time 134 whilethe entrance-side circuit board detect sensor 111 is detecting thecircuit board 2 subsequent to the transfer by the transfer conveyor 110as shown in FIG. 3A, and obtains a circuit board length in the transferdirection of the circuit board 2 from the circuit board detect time 134.In other words, since the control device 118 recognizes the speed of thetransfer conveyor 111 beforehand, the control device obtains the circuitboard length of the circuit board 2 on the basis of the circuit boarddetect time 134 as is understood from FIG. 3B.

In step 3, the control device 118 obtains the transfer estimate timebased on the obtained circuit board length of the circuit board 2, thepreliminarily recognized transfer speed of the transfer conveyor 110,and a preliminarily detected distance between the entrance-side circuitboard detect sensor 111 and the exit-side circuit board detect sensor112. More specifically, the control device 118 subtracts the circuitboard length of the circuit board 2 from the distance between thesensors 111 and 112, thereby obtaining a transfer distance, and dividesthe transfer distance by the transfer speed of the transfer conveyor110, whereby the transfer estimate time is obtained. Since a pluralityof circuit boards are generally carried into the reflow solderingapparatus 101 in a single line, each of the transfer estimate times isobtained in the same way for each of the carried circuit boards. Theobtained transfer estimate times are stored separately for each circuitboard to be monitored into the memory part 1181 of the control device118. The transfer estimate time can be obtained with taking a slip, ahitch or the like of the circuit board 2 in the middle of the transferinto account. The calculated values are stored in the memory part 1181as empirical correction data. An accuracy of the transfer estimate timecan be improved more by using the correction data. Since a memorycapacity of the memory part 1181 is limited, as to the monitored circuitboard 2 passing through the entrance-side circuit board detect sensor111 and exceeding the transfer estimate time, the control device 118eliminates data of the transfer estimate time of the monitored circuitboard 2 after the monitored circuit board 2 is judged as to whether itis transferred normally or abnormally. Thus a memory area for a freshcircuit board 2 to be monitored is secured.

In next step 4, the control device 118 monitors a past time that elapsessince the entrance-side circuit board detect sensor 111 finishesdetecting the circuit board 2 and monitors whether or not the exit-sidecircuit board detect sensor 112 detects the monitored circuit board 2within the circuit board detect time 134 corresponding to the circuitboard length after the monitored past time exceeds the transfer estimatetime. That is, the circuit board detect time 134 serves as an allowancetime for the exit-side circuit board detect sensor 112 to detect thecircuit board 2. The circuit board detect time 134 is a timecorresponding to the circuit board length of one circuit board 2 by wayof example. In the first embodiment as described above, the circuitboard detect time 134 is added immediately after a time point when thetransfer estimate time has passed. However, as the allowance time, forexample half the circuit board detect time 134 may be provided beforeand after the time point when the transfer estimate time is completedrespectively. How to arrange and distribute the circuit board detecttime 134, namely, the allowance time to the time point when the transferestimate time is complete can be set on a case-by-case basis. Inaddition, the allowance time is not limited to the circuit board detecttime 134 although the circuit board detect time 134 is utilized in theembodiment.

In step 4, when the exit-side circuit board detect sensor 112 detectsthe circuit board 2 within the allowance time, the control device 118judges that the circuit board 2 is transferred normally by the transferconveyor 110. On the other hand, unless the exit-side circuit boarddetect sensor 112 detects the circuit board 2, the control device judgesthat the transfer of the circuit board 2 is abnormal.

The operation when the transfer is judged as abnormal in step 4 will bedepicted with reference to FIG. 4.

The control device 118 starts the circuit board discharge conveyor 115via the driving source 120 for the circuit board discharge conveyor instep 5. A time while the circuit board discharge conveyor 115 operatesis set so that the dropped circuit board 133 can be discharged outsideof the reflow soldering apparatus 101 even if the circuit board 2 dropssomewhere during the transfer by the transfer conveyor 110. In thepresent embodiment, the circuit board discharge conveyor 115 is startedin step 5 when the transfer is judged as abnormal in step 4. The circuitboard discharge conveyor 115 operates only for a necessary time asabove, and therefore energy can be saved. However, the present inventionis not restricted to this arrangement and the circuit board dischargeconveyor 115 may be maintained in an operating state irrespective ofpresence or absence of the transfer abnormality in step 4.

In step 6, when the circuit board discharge completion detect sensor 117detects the dropped circuit board 133 while the circuit board dischargeconveyor 115 is operating, the control device 118 judges that thetransfer abnormality is a drop of the circuit board 2, displaying to thedisplay device 121 that the drop takes place. On the other hand, if thecircuit board discharge completion detect sensor 117 does not detect thedropped circuit board 133 in step 6, the control device 118 judges instep 7 whether or not the exit-side circuit board detect sensor 112detects a circuit board 3 carried into the reflow soldering apparatus101 next to the circuit board 2. When the exit-side circuit board detectsensor 112 does not detect the circuit board 3, the control device 118judges that the above transfer abnormality is a jam and makes thedisplay device 121 display generation of the jam. In addition, thecontrol device 118 lowers a temperature of the heating furnace 122 orstops the heating of the heating furnace 122. To the contrary, when thecircuit board discharge completion detect sensor 117 does not detect thedropped circuit board 133 during the operation of the circuit boarddischarge conveyor 115 and the exit-side circuit board detect sensor 112detects the circuit board 3, the control device 118 judges that thetransfer abnormality is a wrong judgment, without displaying to thedisplay device 121.

When a transfer state is monitored with use of the transfer estimatetime as above, the transfer abnormality of the circuit board 2 can bedetected regardless of a thickness of the circuit board 2.

Effects as follows are also exerted if it is judged on the basis of themeasured circuit board length of the circuit board 2 whether or not thecircuit board is transferred normally by the transfer conveyor 110.Specifically, a time between when the circuit board completely entersthe apparatus entrance 131 and when a leading end of the circuit board 2reaches the apparatus exit 132 can be calculated by measuring thecircuit board length. As a result, influences caused by a feed conveyorarranged at the entrance of the reflow soldering apparatus 101 andpushing the circuit board 2 into the reflow soldering apparatus 101, andcaused by a take-out conveyor arranged at the exit of the reflowsoldering apparatus 101 and pulling the circuit board 2 outside from theapparatus 101 are eliminated. Also for instance, a necessity formonitoring and occurrence of malfunctions or the like can be eliminated.

Furthermore, in the case where a relationship between the circuit boardlength of the circuit board 2 and a temperature required for operatingthe reflow soldering to the circuit board 2 is already known,temperatures of preheating and actual heating carried out by the reflowsoldering apparatus 101 may be changed with use of the information onthe circuit board length.

By adopting the constitution of the first embodiment, whether thetransfer abnormality is a jam or a drop of the circuit board 2 in themiddle of the transfer by the transfer conveyor 110 can be judged.

Since the memory part 1181 stores the transfer estimate time for everyindividual circuit board 2 carried into the reflow soldering apparatus101, the presence or absence of the transfer abnormality can be judgedfor each circuit board 2.

Moreover, since the entrance-side circuit board detect sensor 111 notonly detects whether the circuit board is carried in or not, butmeasures the circuit board length, a parts count is reduced and costscan be lowered.

According to the first embodiment, the transfer estimate time is set tobe the time between when the circuit board 2 passes the entrance-sidecircuit board detect sensor 111 and when the circuit board 2 reaches theexit-side circuit board detect sensor 112. However, the transferestimate time can be a time which elapses between when the circuit board2 is detected by the entrance-side circuit board detect sensor 111 andwhen it is detected by the exit-side circuit board detect sensor 112, ora time which elapses between when the circuit board 2 is detected by theentrance-side circuit board detect sensor 111 and when the circuit board2 passes the exit-side circuit board detect sensor 112 at the exit time.

Second Embodiment

FIG. 5 shows a reflow soldering apparatus 102 according to a secondembodiment, in which the same parts as in the reflow soldering apparatus101 of the above first embodiment are designated by the same referencenumerals. In comparison with the reflow soldering apparatus 101 in thefirst embodiment, the reflow soldering apparatus 102 of the instantembodiment is not equipped with the speed detector 116 for the transferconveyor and the control device 118 is changed to a control device 141.The control device 141 includes a memory part 1411, but does not havethe monitor part 1182. The reflow soldering apparatus 102 is not changedin any other constitution.

The reflow soldering apparatus 102 operates in a manner as will bedescribed hereinbelow.

The driving source 119 for the transfer conveyor drives the transferconveyor 110 in accordance with a command from the control device 141.Subsequent to the driving, in step 11 in FIG. 7, the control device 141measures a time, as indicated in FIGS. 6A and 6A, which elapses betweenwhen the circuit board 2 passes the entrance-side circuit board detectsensor 111 and when the next circuit board 3 to the circuit board 2passes the entrance-side circuit board detect sensor 111. The time isstored as a carry-in interval into the memory part 1411. When three ormore circuit boards are sequentially carried in, each carry-in intervalof circuit boards is sequentially measured and stored in the memory part1411.

In next step 12, a time which elapses between when the exit-side circuitboard detect sensor 112 detects an object to be detected, i.e. thecircuit board 2, transferred by the transfer conveyor 110 and when theexit-side circuit board detect sensor 112 detects the next transferredcircuit board 3 is measured, and then the measured time is set as adischarge interval. In the case where three or more circuit boards aresequentially carried in as mentioned above, each discharge interval ofcircuit boards is sequentially measured and stored in the memory part1411.

In step 13, the control device 141 compares the carry-in interval andthe discharge interval, and judges that the circuit boards 2 and 3 arenormally transferred when the comparison result is within an allowablerange. The allowable range can be determined with a slip or a snag ofthe circuit boards in the middle of the transfer taken into account. Thethus-set allowable range of empirical values is stored as correctiondata in the memory part 1411. An accuracy of the comparison resultbetween the carry-in interval and the discharge interval can be improvedmore by using the correction data. The allowable range is, e.g., alength corresponding to the circuit board length of one circuit board 2.By contrast, the control device 141 judges that the transfer by thetransfer conveyor 110 is abnormal when the comparison result is not inthe allowable range.

In the case of three or more circuit boards transferred, each carry-ininterval and discharge interval are compared, whereby the presence orabsence of the transfer abnormality is judged for each case.

The operation described with reference to FIG. 4 is executed when thetransfer abnormality is brought about. Since the two circuit boards 2and 3 transferred adjacently are objects to be detected in the secondembodiment, the control device 141 judges in step 6 that the transferabnormality is caused by the “drop” when the circuit board 2 or 3 isdetected. On the other hand, the control device 141 judges in step 7that the transfer abnormality results from the “jam” when the exit-sidecircuit board detect sensor 112 detects neither the circuit board 2 northe circuit board 3.

As above, a transfer state is monitored with use of the interval betweenthe circuit boards. Thus the transfer abnormality of the circuit board2, or both circuit boards 2 and 3 can be detected irrespective of athickness of the circuit board 2, or irrespective of thicknesses of thecircuit boards 2 and 3. Similar to the first embodiment, the secondembodiment enables to judge whether the transfer abnormality is causedby the jam, in other words clog, or by the drop of the circuit board 2in the middle of the transfer by the transfer conveyor 110. Effectivelythe judgment is not influenced by a speed of the transfer conveyor 110.

The memory part 1411 stores the carry-in interval and the dischargeinterval for each circuit board 2, so that the presence or absence ofthe transfer abnormality can be judged for each circuit board 2.

Furthermore, the entrance-side circuit board detect sensor 111 not onlydetects whether or not the circuit board is carried in, but measures theinterval of the carried circuit boards, while the exit-side circuitboard detect sensor 112 not only detects whether or not the circuitboard is discharged, but measures the interval of the carried-outcircuit boards. This arrangement can reduce the number of parts andcost.

The above description is related to a case where the interval of twocircuit boards 2 and 3 transferred adjacently is smaller than a distancebetween the entrance-side circuit board detect sensor 111 and theexit-side circuit board detect sensor 112. If the interval of a circuitboard supplied to the transfer conveyor 110 is longer than the distanceof the sensors, that is, if the number of the circuit board present inthe reflow soldering apparatus 102 is one, an embodiment of the presentinvention is so constituted that the control device 141 judgesoccurrence of the transfer abnormality unless the exit-side circuitboard detect sensor 112 detects the circuit board 2 within a fixed timeafter the circuit board 2 has passed the entrance-side circuit boarddetect sensor 111.

The aforementioned fixed time is a time necessary for the circuit board2 to reach the exit-side circuit board detect sensor 112 after havingpassed the entrance-side circuit board detect sensor 111. At theoccurrence of the transfer abnormality, if the circuit board dischargecompletion detect sensor 117 detects the circuit board 2 while thecircuit board discharge conveyor 115 is driving, the control device 141judges that the transfer abnormality is the “drop” and displays to thedisplay device 121 that the circuit board drops. On the other hand, ifthe circuit board discharge completion detect sensor 117 does not detectthe circuit board 2 while the circuit board discharge conveyor 115 isdriving, the control device 141 judges that the transfer abnormality isthe “clog” in other words “jam”, with displaying occurrence of the clogto the display device 121. At the same time, the control devicedecreases a temperature of the heating furnace 122 or stops the heatingfurnace.

According to the second embodiment, the carry-in interval is the timewhich elapses between when the circuit board 2 passes the entrance-sidecircuit board detect sensor 111 and when the circuit board 3 passes theentrance-side circuit board detect sensor 111 as described above.However, the interval may be a time which elapses between when theentrance-side circuit board detect sensor 111 detects the circuit board2 and when the entrance-side circuit board detect sensor 111 detects thecircuit board 3.

Third Embodiment

FIG. 8 shows a reflow soldering apparatus 103 according to a thirdembodiment of the present invention, wherein the same parts aredesignated by the same reference numerals as in the reflow solderingapparatus 101 in the first embodiment. The reflow soldering apparatus103 in the third embodiment does not have the speed detector 116 for thetransfer conveyor, unlike the reflow soldering apparatus 101 of thefirst embodiment. Instead, a counter device 152 is installed whichincrements a count value by one in accordance with a signal from theentrance-side circuit board detect sensor 111 every time the circuitboard is carried to the apparatus entrance 131, and decrements the countvalue by one based on a signal from the exit-side circuit board detectsensor 112 every time the circuit board is discharged to the apparatusexit 132. The control device 118 is changed to a control device 151which has a memory part 1511 and does not have a monitor part 1182. Thethird embodiment is not different in other points of the constitution.

The operation of the reflow soldering apparatus 103 will be depictedbelow.

The driving source 119 for the transfer conveyor drives the transferconveyor 110 in compliance with a command from the control device 151.

In step 21 of FIG. 10, the number of circuit boards 2 that can bepresent between the circuit board detect sensors 111 and 112 is set as acircuit board count set value to the counter device 152. In step 22, asshown in FIG. 9, one is added to the count value of the counter device152 when the entrance-side circuit board detect sensor 111 detects thecircuit board 2, and one is subtracted from the count value when theexit-side circuit board detect sensor 112 detects the circuit board 2.In step 23, the count value of the counter device 152 after the transferconveyor 110 starts transferring the circuit boards 2 is compared withthe circuit board count set value set to the counter device 152 in step21. When the count value of the counter device 152 is not smaller thanthe set value, the control device 151 judges that the circuit boardtransfer by the transfer conveyor 110 is abnormal, with displayingoccurrence of the abnormality to the display device 121. If the countvalue of the counter device 152 is smaller than the set value, thecontrol device 151 judges that the transfer conveyor 110 normallytransfers the circuit boards 2.

In the case where the transfer abnormality is judged by the controldevice 151, the operation described with reference to FIG. 4 is executedsimilar to the first and second embodiments.

The number of circuit boards transferred is used as a judgment elementfor the transfer abnormality as above, so that the abnormality duringthe transfer can be detected.

Since the transfer state is monitored with use of information on thenumber of circuit boards, the transfer abnormality of the circuit board2 can be detected irrespective of the thickness of the circuit board 2in the same way as in the first and second embodiments describedearlier. Moreover, whether the transfer abnormality results from theclog or the drop of the circuit board 2 in the middle of the transfer bythe transfer conveyor 110 can be judged as well.

Although the counter device 152 has a comparing and operating functionin the above description, the comparison and operation may be carriedout by the control device 151.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

What is claimed is:
 1. A reflow soldering apparatus comprising: atransfer conveyor for transferring a circuit board with electroniccomponents from an entrance to an exit of the reflow soldering apparatushaving a heating furnace through which the circuit board mounted ispassed so as to operate reflow soldering to the electronic components onthe circuit board; an exit-side circuit board detect sensor arranged atthe exit for detecting that the circuit board transferred by thetransfer conveyor is carried into the reflow soldering apparatus; adischarge conveyor arranged below the transfer conveyor for discharginga dropped circuit board dropped from the transfer conveyor during thetransfer by the transfer conveyor from an inside to an outside of thereflow soldering apparatus; a discharge completion detector arranged atan exit side of the discharge conveyor for detecting that the droppedcircuit board transferred by the discharge conveyor is discharged to theoutside of the reflow soldering apparatus; and a control device whichjudges based on information from the exit-side circuit board detectsensor whether or not the circuit board is transferred by the transferconveyor from the entrance to the exit, controls the discharge conveyorto discharge the dropped circuit board when judging occurrence oftransfer abnormality, determines that the transfer abnormality is thedrop of the circuit board when the discharge completion detector detectsthe dropped circuit board, and then continues the reflow soldering whendetermining the drop.
 2. The reflow soldering apparatus according toclaim 1, in the case where a plurality of circuit boards are carried tothe entrance in a single line, the control device determining that thetransfer abnormality is a jam of the circuit boards at the transferconveyor and then lowering a temperature of the heating furnace when thedischarge completion detector does not detect discharge of the droppedcircuit board and moreover the exit-side circuit board detect sensordoes not detect discharge of the circuit board.
 3. The reflow solderingapparatus according to claim 1, further comprising an entrance-sidecircuit board detect sensor arranged at the entrance for detecting thatthe circuit board is carried into the apparatus, wherein the controldevice has a transfer estimate time necessary for the transfer conveyorto transfer the circuit board from the entrance to the exit, so that thecontrol device judges presence or absence of the transfer abnormality ona basis of whether or not the exit-side circuit board detect sensordetects discharge of the circuit board within a circuit board detecttime after the transfer estimate time has passed, the circuit boarddetect time corresponding to a passing time of the circuit board in atransfer direction of the circuit board detected by the entrance-sidecircuit board detect sensor.
 4. The reflow soldering apparatus accordingto claim 2, further comprising an entrance-side circuit board detectsensor arranged at the entrance for detecting that the circuit board iscarried into the apparatus, wherein the control device has a transferestimate time necessary for the transfer conveyor to transfer thecircuit board from the entrance to the exit, so that the control devicejudges presence or absence of the transfer abnormality on a basis ofwhether or not the exit-side circuit board detect sensor detectsdischarge of the circuit board within a circuit board detect time afterthe transfer estimate time has passed, the circuit board detect timecorresponding to a passing time of the circuit board in a transferdirection of the circuit board detected by the entrance-side circuitboard detect sensor.
 5. The reflow soldering apparatus according toclaim 1, further comprising an entrance-side circuit board detect sensorarranged at the entrance for detecting that the circuit board is carriedinto the apparatus, wherein, in the case where a plurality of circuitboards are carried to the entrance in a single line, the control devicejudges presence or absence of the transfer abnormality based on acomparison between a carry-in interval of adjacent circuit boardsdetected by the entrance-side circuit board detect sensor and adischarge interval of the adjacent circuit boards detected by theexit-side circuit board detect sensor.
 6. The reflow soldering apparatusaccording to claim 2, further comprising an entrance-side circuit boarddetect sensor arranged at the entrance for detecting that the circuitboard is carried into the apparatus, wherein, in the case where aplurality of circuit boards are carried to the entrance in a singleline, the control device judges presence or absence of the transferabnormality based on a comparison between a carry-in interval ofadjacent circuit boards detected by the entrance-side circuit boarddetect sensor and a discharge interval of the adjacent circuit boardsdetected by the exit-side circuit board detect sensor.
 7. The reflowsoldering apparatus according to claim 1, further comprising anentrance-side circuit board detect sensor arranged at the entrance fordetecting that the circuit board is carried into the apparatus, and acounter device in which a circuit board count set value is defined andwhich adds one when the entrance-side circuit board detect sensordetects the circuit board and subtracts one when the exit-side circuitboard detect sensor detects the circuit board, the circuit board countset value corresponding to the number of circuit boards which can bepresented between the entrance-side circuit board detect sensor and theexit-side circuit board detect sensor, so that the control device judgespresence or absence of the transfer abnormality on a basis of acomparison between the circuit board count set value and a countedcircuit board value by the counter device.
 8. The reflow solderingapparatus according to claim 2, further comprising an entrance-sidecircuit board detect sensor arranged at the entrance for detecting thatthe circuit board is carried into the apparatus, and a counter device inwhich a circuit board count set value is defined and which adds one whenthe entrance-side circuit board detect sensor detects the circuit boardand subtracts one when the exit-side circuit board detect sensor detectsthe circuit board, the circuit board count set value corresponding tothe number of circuit boards which can be presented between theentrance-side circuit board detect sensor and the exit-side circuitboard detect sensor, so that the control device judges presence orabsence of the transfer abnormality on a basis of a comparison betweenthe circuit board count set value and a counted circuit board value bythe counter device.